1. Field of the Invention
The present invention relates to a process of semicontinuously producing aniline condensed dyes using a multistage reaction system.
2. Description of the Prior Art
It is well known in the art that in many chemical processes batch operation is more convenient than continuous operation. However, since in a batch process various conditions such as temperature, concentration and the like vary during operation, a substantial amount of operator attention is needed to control the operation, and batch operation, in this respect, is more difficult than continuous operation. Moreover, batch operation has the defect that the quality of the products obtained tends to vary from batch to batch.
Still further, in batch operation the efficiency drops as the member of reaction steps in which the temperature differs increases or as the reaction temperature in each reaction step is increased. That is, when the number of reaction steps increases, operation control becomes difficult, and when the reaction temperature is high, the time for preheating and after-cooling the reaction vessel(s) is prolonged. Thus, an increase in the operation time per batch occurs.
Condensed dyes obtained by the condensation of aniline and nitrobenzene (and/or alkylanilines, alkylnitrobenzenes, diazoaminobenzene, etc.) in the presence of catalysts such as hydrochloric acid and iron chloride are generally called "Spirit Black," "Nigrosine," "Induline," etc., and are widely used as coloring materials for synthetic resins, printing inks, etc. In particular, the annual production of Spirit Black amounts to more than 10,000 tons per year.
Since the reaction of these aniline condensed dyes requires the use of a catalyst having high corrosiveness, such as hydrochloric acid and iron chloride, and is carried out at high temperatures, specific reaction vessels such as a glass-lined reaction vessels are required. In many cases, reaction vessels constructed of materials susceptible to heat shock are used so that a rapid increase or reduction in temperature or a great temperature difference between the reaction vessel wall and the reaction solution charged or heating media introduced into a jacket of reaction vessel, each of which can destroy the reaction vessel, must be avoided.
Thus, in the production of aniline condensed dyes by a batch procedure, high operator skill is required for temperature control, and production efficiency is markedly reduced.
In order to avoid these disadvantages, various continuous reactions have been proposed. However, in continuous reactions, a complicated reaction system is required, a long period of time at high temperatures is needed, the construction materials for the reaction vessel are limited, and the like. Further, even if a large amount of money is expended to provide a complete, continuous reaction apparatus, the amount of product to be sold which permits one to recover the money expended is extremely high. Under such circumstances, currently production of such materials is only by batch procedures.